"Whenever we needed help, he would help us with whatever we need –- advice, studies, anything," Abu Baker, 16, whom Smith tutored, told ABC News. "He was an amazing guy. He was really funny. He had the most amazing sense of humor."

The White House said President Obama was briefed this morning on the killing, and the State Department said it had been in touch with Smith's family. The FBI is investigating the incident, although it is unclear whether Smith was targeted because he was American.

"We are following events closely, and at this point no individual or group has claimed responsibility," White House Press Secretary Jay Carney told reporters today. "We look to the Libyan government to thoroughly investigate this killing."

Smith's wife, Anita, and young son Housea lived full-time in Benghazi but had returned for the winter holiday a few days ago, Hodge said. Smith, a fluent Arabic speaker, was expected to join them at the end of this week, he said.

Smith left school today for a couple of hours to go for a jog, Hodge said. Fitness was important to Ronnie, and he shared that with his Libyan students, often leading exercises with them after school, he said.

But today he was alone on his run through the neighborhood near the school when he was killed, according to Hodge.

"I think it was an opportunist, someone who just happened to see him there," he said. "There's no way they could have known he would be there at that time."

Three other Americans were teaching at the International Benghazi School, which has 650 students from kindergarten through high school--the majority Libyan, Hodge said.

The expats have generally felt safe in Benghazi, Hodge said.

Smith, Hodge said, was in the country because he believed in the possibility of change there and in the lives of the children he taught.

"He was dedicated. He always put the students first," Hodge said. "He wanted to make a difference. And he did."

Since Libyan dictator Moammar Gadhafi was toppled in 2011, the security situation in Libya has deteriorated, with armed militias controlling large swathes of the country.

"It's a very good situation as far as education is concerned," Hodge said. "It's a very sad situation as far as security situation is concerned."